Avoidant Personality Disorder (APD) is characterized by long-standing avoidance of social interaction and extreme fears of criticism, humiliation, and rejection. APD is the most common personality disorder among patients with social phobia and panic disorder with agoraphobia and is prevalent among depressed patients as well. APD may be related to poor treatment outcome with psychological as well as pharmacological treatment of panic disorder, and is of interest in its own right as a disorder that interferes with effective social functioning. Research on APD has been hampered by changing diagnostic criteria, the lack of adequately validated diagnostic instruments, and the paucity of basic empirical research on the psychopathology of this disorder. Two studies are proposed to address issues in the assessment of APD. In Study 1 (a) the effects of short-term treatment for an Axis I disorder (agoraphobia) on the stability of the diagnosis of APD will be examined in a sample of 40 patients; and (b) and replication of a previous study wherein APD predicted poor treatment response for agoraphobia in this program will be conducted. In Study 2, the responses of two groups of generalized social phobic patients (26 with APD and 26 without) will be contrasted on behavioral and self-report measures of social phobia and APD. This study will serve as a pilot for a projected treatment study on APD and for a larger psychopathology study to determine whether APD can be empirically and usefully distinguished from the Axis I disorder of generalized social phobia. Finally, the pooled samples of Studies 1 and 2 will be used to examine (a) the interrater and test-retest reliability of APD measures, and (b) the concurrent validity of self-report, relatives' report, and interview measures of APD.